Recessed tread wear indicator

ABSTRACT

A tread band having a primary groove opening onto a front face of the tread band, a secondary feature molded into the tread band, and a wear indicator molded into a section of an undertread portion of the tread band. The wear indicator is useful for providing an end-of-useable tread indication when the front face of the tread band wears even with a top portion of the wear indicator. Furthermore, the secondary feature may be characterized as opening onto a back face of the tread band, a side face of the tread band or combinations thereof. The section of the undertread portion may extend less than about 4 mm or less than about 3 mm from the back face of the tread band. In other embodiments, the section of the undertread portion may extend less than about 1.5 mm from the back face of the tread band.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to tires and more particularly, to tiretread wear indicators.

2. Description of the Related Art

It is known how to provide wear detectors on the tread pattern elementsof a tire tread for motor vehicles. One example of a tread wearindicator is shown in FIGS. 1A-C. A tread band 10 includes grooves 13opening from the front face of the tread band 10, these grooves 13forming the treads of the tread band 10. Wear indicators 11 are moldedinto the grooves 13 at a depth m 12, which represents the minimumacceptable depth of the tread grooves 13. FIG. 1B shows the tread band13 worn down to the wear indicators 11, indicating that the tread band10 has served its useful life. FIG. 1C is a perspective view of thetread band 10 showing that the tread wear indicators 11 are generallylocated at the same circumferential location along the tread band 10 sothat when the tread is worn down to the wear indicators 11, a wear bar14 is formed laterally across the tread band 10, which indicates thatthe useful life of the tread is ended. The undertread 16 portion of thetread band 10 is that portion that is below the bottom of the grooves 13that are formed in and open to the front face 17 of the tread band 10.

Other examples, of tread wear indicators may be found, for example, inthe British patent publications GB-A-2 330 808 and GB-A-2 268 715. Thesereferences disclose visual wear detectors consisting of layers ofcolored light-reflecting rubber that are disposed over the entirecircumference of the tire in the mass of the tread. These colored rubberindicators become visible following a given amount of wear on the tirethat strips away the rubber covering the colored rubber layers.

Tread bands are used for retreading tires as well as in new tireconstruction. In either case, the tread band is bonded to a tire casingto provide either a new tire (when bonded to a new tire casing) or aretread tire (when bonded to a used tire casing that has had the oldtread buffed off). The tread bands are molded and may be either cured oruncured before being bonded to the tire casing.

The undertread portion of the tread band is typically 2-5 mm thick andmay facilitate demolding the tread band. It may further assist inresisting lateral compression of the tread pattern during the process ofbonding the tread band to the tire casing. However, this undertread doesnot provide any useful life for the tread because it lies below thetread grooves that open to the front face of the tread band.

While wear bars are useful indicators of the end of the useful life forthe tread, there is a need for improved tread wear indicators thatmaximize the use of the entire tread band before its end of life.

SUMMARY OF THE INVENTION

One embodiment of the present invention includes a tread band having aprimary groove opening onto a front face of the tread band, a secondaryfeature molded into the tread band, and a wear indicator molded into asection of an undertread portion of the tread band. The wear indicatoris useful for providing an end-of-useable tread indication when thefront face of the tread band wears even with a top portion of the wearindicator. Furthermore, the secondary feature may be characterized asopening onto a back face of the tread band, a side face of the treadband or combinations thereof.

In particular embodiments of the present invention, the section of theundertread portion may extend less than about 4 mm or less than about 3mm from the back face of the tread band. In other embodiments, thesection of the undertread portion may extend less than about 1.5 mm fromthe back face of the tread band.

The tread band of the present invention further includes embodimentswherein the wear indicator extends radially from the back face of thetread band and is molded into an indicator portion of the secondaryfeature.

The present invention further provides embodiments that include a tirehaving a tire carcass having a crown portion with a tread band bonded tothe crown portion, the tread band having the features described above.Particular embodiments of the present invention include tires that arenew as well as tires that are re-treaded with a tread band as describedabove.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawing wherein like reference numbers representlike parts of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-C are drawings showing cross sectional and perspective views ofa tread band showing a wear bar as known in the prior art.

FIGS. 2A-2B are drawings showing cross sectional views of a tread bandhaving a wear indicator extending radially from the back face of thetread band and molded into the secondary grooves in accordance with aparticular embodiment of the present invention.

FIG. 2C is a top view of a portion of the tread band having the wearindicator of FIGS. 2A-2B.

FIGS. 3A-3B are drawings showing perspective views of a top and bottommold suitable for molding a tread band having a wear indicator moldedinto the secondary grooves.

FIG. 3C is a drawing of a perspective view of a detail of the wearindicator portions of the top and bottom molds that are shown in FIGS.3A-3B.

FIGS. 4A-4B are drawings of perspective and cross sectional views of atread band having a wear indicator molded into a cavity that is open tothe front face of the tread band.

FIG. 5 is a drawing of a perspective view of a portion of a retread tirehaving a tread band in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a wear indicator molded into theundertread portion of a tread band to provide an end-of-usable-treadindication. Such indication is provided when the front face of the treadband wears even with a top portion of the wear indicator. The tread bandincludes both a primary feature that opens onto a front face of thetread band and at least one secondary feature molded into the tread bandthat opens onto a back face of the tread band, a side face of the treadband or combinations thereof. Primary and secondary features mayinclude, for example, sipes, holes and/or grooves as known to thosehaving ordinary skill in the art.

Treads on tires reach an end-of-usable tread when the total tread depthprovided by the features that are open to the front face of the treadare below an acceptable minimum depth or below an acceptable totalvolume. Such minimum depth and/or volume may be set by regulation in agiven jurisdiction or alternatively, may be determined by the tiredesigner.

The wear indicator of the present invention is molded into theundertread portion of the tread band to provide an end-of-usable-treadindication for the secondary features. Since the secondary features aremolded into the tread band and are open to the sides and/or back of thetread band, these secondary features do not provide usable tread depthor volume until the front face is worn to a depth that opens thesecondary features to the front face. As the primary features that areopen to the front face wear away, the secondary features become exposedand open to the front face to provide the required open volume and/ordepth in the tread. This allows the tread band to be worn much closer tothe rear face of the tread band, allowing more of the tread band to beutilized before the tire is discarded or retreaded. Preferably the wearindicator is molded into a section of the undertread portion, thesection extending less than about 4 mm from the back face of the treadband. More preferably the section may extend less than about 1.5 mm fromthe back of the tread band. Alternatively, the section may extend lessthan about 3 mm from the back face of the tread band. It should be notedthat since the tread band is typically bonded to a tire carcass, the“radial” direction of the tread band as used herein is in theperpendicular direction between the front face and the back face of thetread band.

As disclosed above, the wear indicator that is molded into the treadband provides an end-of-usable-tread indication when the front face ofthe tread band wears even with a top portion of the wear indicator. Thetop portion of the wear indicator may be, for example, a front or topsolid face of the molded indicator or the top or front of a void spacemolded into the tread band. For example, a series of small perforationsmay be molded into a section of the undertread in a pattern that spellsout “WORN.” When the front face of the tread band is worn to thatsection of the undertread, the “WORN” indication will become visible,thereby providing the end-of-usable-tread indication. Solid wearindicators may be characterized as “positive” indicators and wearindicators that consist of voids may be characterized as “negative”indicators. However, whether the indicators are positive or negativeindicators, the indication provided to the user of the tires is thesame, i.e., that the end-of-useable-tread has been reached.

In a particular embodiment of the present invention, the wear indicatorextends radially from the back face of the tread band to a predeterminedminimum tread depth and is molded into a portion of one or moresecondary features that open onto a back or side face of a tread band.

In another particular embodiment, the top surface of the wear indicatoris exposed in a cavity that extends from the front face of the treadband to below the top face of the wear indicator. When the tread wearsdown to expose the wear indicators, the end of the useful life of thetread band is indicated. Advantageously, the wear indicator of thepresent invention is typically located in the undertread of the primaryfeatures that open onto the front face of the tread band so that agreater amount of the undertread can be utilized as useful tread,thereby extending the useful life of the tread band.

Particular embodiments of the present invention include a tread bandthat may be bonded either to a new tire casing or to a used tire casing.Bonding the tread band to a used tire casing that has had the old treadbuffed off is part of the retread process. The tread band is molded withfeatures that are formed by both the top and bottom sections of themold. The top mold section molds one or more primary features that areopen to the front face of the tread band and the bottom mold sectionmolds one or more secondary features that are open to the back face ofthe tread band. Optionally, other secondary features may be molded byother molding elements, i.e., molds that interact with the top andbottom mold sections to form a complete mold as known to those havingordinary skill in the art, to form features that, for example are opento one or more sides of the tread band.

In particular embodiments of the present invention, the bottoms of theone or more secondary grooves extend to a greater distance radially fromthe back face of the tread band than the groove bottoms of the one ormore primary grooves. This arrangement allows, during the wearing of thetire, the secondary grooves to open to the front face of the tread bandand thereby provide useable features as the primary grooves wear away.It should be noted that the “bottom” of a feature is typically oppositethe open end of the feature.

Since the secondary features provide tread for use after the primaryfeatures have worn away, placing the wear indicator in a portion of thebottom of the primary features does not provide an indication of theminimum tread remaining. Placing the wear indicator in a portion of theprimary feature bottoms would provide the end-of-usable-tread indicationlong before the tread was worn to its minimum acceptable depth becauseit does not take into account the additional tread life that is added byutilizing the secondary features.

In particular embodiments of the present invention, the wear indicatorextends radially from the back face of the tread band to a predeterminedminimum secondary feature depth such that the top portion of the wearindicator lies below the bottom of the primary features. In this manner,as the tread continues to wear past the primary and into the secondaryfeatures, the wear indicator provides the desired end-of-useful-treadindication as the secondary features are worn to their minimumacceptable depth. In a particular embodiment, the wear indicator may bemolded into a portion of the bottoms of the secondary grooves,preferably at the same circumferential location so that as the wearindicators become exposed, they form a wear bar laterally across theface of the tread band. Alternatively, the wear bar may be molded intothe bottom of a cavity that opens onto the top surface of the treadband.

Particular embodiments of the present invention further include anaccess channel opening from the front face of the tread band andextending radially to a top face of a wear indicator that extendsradially from the back of the tread band. If the wear indicator ismolded into a portion of a secondary feature, then preferably the wearindicator is surrounded by barriers, thereby forming a chambersurrounding the wear indicator. The walls that separate the wearindicator from the secondary feature are typically flashing.

The access channel provides access with a measurement device toascertain that the wear indicator is at the correct depth to indicatethe minimum tread depth when showing. Additionally, the access channelprovides a visual indication of the tread wear. The observable presenceof the access channel provides a visual indication that the tire has notworn to its minimum acceptable tread depth. After the access channel hasbeen worn away through normal tread wear during use of the tire, thewear indicator becomes visible, thereby providing a visual indication asto whether the tire has reached its end-of-useable tread condition.

Although the access channel may typically be shaped as a square, thereis no limitation as to the acceptable shapes for the access channel. Forexample, the access channel may be circular, oval, rectangular,triangular, any other regular or irregular polygon shape or combinationsthereof. Furthermore, the access channel may be, without limitation,between about 2 mm and 12 mm wide or preferably, between about 4 mm and6 mm wide.

Particular embodiments of the present invention further include both newand retread tires. Such tires include a tire carcass having a crownportion and a tread band as described above that is bonded to the crownportion of the tire carcass. As known to those having ordinary skill inthe art, the tread band may be either cured or uncured when firststitched to the crown portion of the tire carcass. If cured, then thetread band is stitched to the crown portion of the tire carcass with,for example, cushion gum and then cured so that the cushion cum bondsthe tread band securely to the crown. If uncured, then the tread iscured after being stitched to the crown.

FIGS. 2A-2B are cross sectional views of a tread band having a wearindicator extending radially from the back face of the tread band andmolded into the secondary grooves and FIG. 2C is a top view of a portionof the tread band having the wear indicator. FIG. 2A includes the treadband 20 having a set of primary grooves 13 that open onto the front face24 of the tread band 20 and a set of secondary grooves 21 that open ontothe back face 12 of the tread band 20. The wear indicator 22 is moldedinto a portion of the bottoms of the secondary grooves 21 and the wearindicator 22 extends radially from the back face 12 of the tread band 20to the minimum groove depth m 26. An access channel 23 is open from thefront face 24 of the tread band 20 to the secondary grooves 21. Theaccess channel 23 provides access for a measuring device to measure thedepth of the wear indicator 22. The access channel 23 further provides avisual indication that the tread depth has not reached the minimumacceptable depth because as long as the open access channel 23 isvisible, the wear indicator 22 has not been reached.

FIG. 2B is a cross sectional view of the tread band shown in FIG. 2Aafter the band has been worn and the primary grooves 13 have nearly wornaway. The bottoms of the secondary grooves 21 are shown opening to thetop face 24 of the tread band 20 to provide useful tread to replace theworn primary grooves 13. The wear indicator 22 becomes visible throughthe opening into the secondary grooves 21 to a person inspecting thetire. It should also be noted that at this point, the access channel 23has worn away and is no longer necessary since the wear indicator 22 isvisible through the bottom of the secondary grooves 21.

FIG. 2C is a top view of a portion of the tread band having the wearindicator as shown in FIGS. 2A-2B. The wear indicator 22 is molded intothe secondary groove 21 and barriers 27 are formed within the secondarygroove 21 to isolate the wear indicator 22 from the adjacent portions ofthe secondary groove 21. The barriers 27 may be flashing depositedwithin the secondary grooves during the molding process oralternatively, may be a molded feature. The barriers 27 prevent moistureand dirt from passing through the access channel 23 into the secondarygroove 21.

FIGS. 3A-3B are perspective views of a top and bottom mold formssuitable for molding a tread band having a wear indicator molded intothe secondary grooves. It should be noted that the solid portions on theinterior of the mold will result in rubber-free portions in the moldedtread band while the void portions of the interior of the mold willresult in solid rubber portions in the molded tread band.

The top mold form 30 shown in FIG. 3A provides the primary groove form31 and the access channel form 32 for molding the primary grooves 13 andthe access channels 23 as shown in FIG. 2A. The top mold form 30 furtherprovides the front face form 33 that forms the front face 24 of themolded tread band.

The bottom mold form 40 shown in FIG. 3B provides the secondary grooveform 41 and the tread wear indicator form 42, which fills with rubberduring the molding process to form the tread wear indicator 22, as shownin FIG. 2A. The access channel form 32 of the top mold aligns with andfills the gap above the tread wear indicator form 42 as shown in FIG.3C. The distance between the bottom of the access channel form 32 andthe back face form 43 is the distance m 26, which is the minimumallowable tread depth as shown in FIG. 2A.

FIGS. 4A-4B are perspective and cross sectional views of a tread bandhaving a wear indicator molded into a cavity that is open to the frontface of the tread band. In this embodiment of the present invention, awear indicator 51 is molded within a cavity 52 that extends from thefront face 54 of the tread band 50 to below the bottom 53 of the primarygrooves 13. As shown in FIG. 4B, the top surface of the wear indicator51 lies below the bottom surface 53 of the primary grooves 13.

FIG. 5 is a drawing of a perspective view of a portion of a retread tirehaving a tread band in accordance with the present invention. Theportion of the retread tire 60 includes a tire carcass 61 having a crownportion 64 to which the tread band 65 is attached. The tread band 65 isattached to the crown portion 64 with cushion gum 62 as known to thosehaving ordinary skill in the art. The openings into the access channels23 provide a visual indication that the tire has not worn beyond itsallowable minimum tread depth.

The terms “comprising,” “including,” and “having,” as used in the claimsand specification herein, shall be considered as indicating an opengroup that may include other elements not specified. The term“consisting essentially of,” as used in the claims and specificationherein, shall be considered as indicating a partially open group thatmay include other elements not specified, so long as those otherelements do not materially alter the basic and novel characteristics ofthe claimed invention. The terms “a,” “an,” and the singular forms ofwords shall be taken to include the plural form of the same words, suchthat the terms mean that one or more of something is provided. Forexample, the phrase “a solution comprising a phosphorus-containingcompound” should be read to describe a solution having one or morephosphorus-containing compounds. The terms “at least one” and “one ormore” are used interchangeably. The term “one” or “single” shall be usedto indicate that one and only one of something is intended. Similarly,other specific integer values, such as “two,” are used when a specificnumber of things is intended. The terms “preferably,” “preferred,”“prefer,” “optionally,” “may,” and similar terms are used to indicatethat an item, condition or step being referred to is an optional (notrequired) feature of the invention.

It should be understood from the foregoing description that variousmodifications and changes may be made in the preferred embodiments ofthe present invention without departing from its true spirit. Theforegoing description is provided for the purpose of illustration onlyand should not be construed in a limiting sense. Only the language ofthe following claims should limit the scope of this invention.

1. A tread band, comprising: a primary groove opening onto a front face of the tread band and a secondary feature molded into the tread band, the secondary feature opening onto at least a back face of the tread band, wherein a bottom of the secondary feature extends to a greater distance radially from the back face than a groove bottom of the primary groove so that the secondary feature bottom is opened to the front face of the tread band prior to disappearance by wear of the primary groove, the opened secondary feature providing groove open volume and depth in the tread; a wear indicator molded into a section of an undertread portion of the tread band to provide an end-of-useable-tread indication for the opened secondary feature when the front face of the tread band wears even with a top portion of the wear indicator, wherein the wear indicator is molded into an indicator portion of the secondary feature and extends radially from the back face of the tread band such that the top portion of the wear indicator is below the secondary feature bottom that opens to the front face of the tread band prior to disappearance by wear of the primary groove, wherein the tread band portion between the top portion of the wear indicator and the secondary feature bottom provides tread depth above the end-of-useable tread indication.
 2. The tread band of claim 1, wherein the section of the undertread portion extends less than about 4 mm from the back face of the tread band.
 3. The tread band of claim 1, wherein the section of the undertread portion extends less than about 3 mm from the back face of the tread band.
 4. The tread band of claim 1, wherein the section of the undertread portion extends less than about 1.5 mm from the back face of the tread band.
 5. The tread band of claim 1, wherein the wear indicator is molded into a plurality of secondary features at the same circumferential location so that a lateral bar comprising a top portion of the wear indicator forms across the tread band as the end-of-usable-tread indication.
 6. The tread band of claim 1, further comprising: an access channel opening from the front face of the tread band and extending radially to a top surface of the wear indicator, wherein the access channel is in fluid communication with the indicator portion of the secondary feature.
 7. The tread band of claim 6, wherein the access channel is not in fluid communication with adjacent portions of the secondary feature that are separated from the indicator portion by a barrier.
 8. The tread band of claim 6, wherein the access channel is between about 4 mm and 6 mm wide.
 9. The tread band of claim 6, wherein the wear indicator molded into the indicator portion of the secondary feature is less than about 12 mm wide.
 10. The tread band of claim 1, wherein the tread band is cured rubber.
 11. The tread band of claim 1, wherein the tread band is uncured rubber:
 12. A tire, comprising: a tire carcass having a crown portion; a tread band bonded to the crown portion of the tire carcass, wherein the tread band comprises: a primary groove opening onto a front face of the tread band and a secondary feature molded into the tread band, the secondary feature opening onto at least a back face of the tread band, wherein a bottom of the secondary feature extends to a greater distance radially from the back face than a groove bottom of the primary groove so that the secondary feature bottom is opened to the front face of the tread band prior to disappearance by wear of the primary groove, the opened secondary feature providing groove open volume and depth in the tread; a wear indicator molded into a section of an undertread portion of the tread band to provide an end-of-useable-tread indication for the opened secondary feature when the front face of the tread band wears even with a top portion of the wear indicator, wherein the wear indicator is molded into an indicator portion of the secondary feature and extends radially from the back face of the tread band such that the top portion of the wear indicator is below the secondary feature bottom that opens to the front face of the tread band prior to disappearance by wear of the primary groove, wherein the tread band portion between the top portion of the wear indicator and the secondary feature bottom provides tread depth above the end-of-useable tread indication.
 13. The tire of claim 12, wherein the tire carcass is cured and the tread band is uncured.
 14. The tire of claim 12, wherein the tread band is stitched to the tire carcass.
 15. The tire of claim 14, wherein the tread band is stitched to the tire carcass with a layer of cushion gum rubber.
 16. The tire of claim 15, wherein the cushion gum rubber is cured to bond the tread band to the tire carcass.
 17. A tread band, comprising: a primary groove opening onto a front face of the tread band and a secondary feature molded into the tread band, the secondary feature opening onto only a back face of the tread band, wherein a bottom of the secondary feature extends to a greater distance radially from the back face than a groove bottom of the primary groove so that the secondary feature bottom is opened to the front face of the tread band prior to disappearance by wear of the primary groove, the opened secondary feature providing groove open volume and depth in the tread; a wear indicator molded into a section of an undertread portion of the tread band to provide an end-of-useable-tread indication for the opened secondary feature when the front face of the tread band wears even with a top portion of the wear indicator, wherein the wear indicator is molded into an indicator portion of the secondary feature and extends radially from the back face of the tread band such that the top portion of the wear indicator is below the secondary feature bottom that opens to the front face of the tread band prior to disappearance by wear of the primary groove, wherein the tread band portion between the top portion of the wear indicator and the secondary feature bottom provides tread depth above the end-of-useable tread indication. 